The present invention relates to a data carrier, and more particularly to a data carrier for use in data processing apparatus.
The use of data carriers which are employed in data processing apparatus is not novel. Generally speaking, it is known to use data carriers in form of tapes or ribbons, or in form of cards. Most commonly the tapes or cards are provided with discrete indicia representing encoded data bits, and these indicia are most commonly formed by punching holes of a selected configuration into the carrier body. When such a carrier is processed in the data processing apparatus, the information represented by the punched holes is retrieved mechanically, electrically or optically. Other data carriers have the information encoded thereon in ways other than by the use of punched holes, for instance by being provided with magnetic layers which are locally magnetized to form magnetized spots on the carrier. Still others have the data bits encoded thereon by printing indicia onto the carrier, for instance with regular ink or magnetic ink.
It should be understood that wherever the term data carrier or carrier body is employed in this specification and in the appended claims, the term is intended to refer to a carrier body capable of being provided with discrete indicia of whatever type, that is, either in form of punched holes, in form of magnetic spots, in form of printed or otherwise applied indicia, or whatever form may already be known from the art.
The prior art uses carriers, such as punched tape or punched cards, which are provided with the discrete indicia arranged in respective rows. In producing such a carrier, that is, in providing it with the rows of holes, it is customary to punch the holes of one row, and then to proceed to punch the holes of another row, and so on. When the carrier is inserted into data processing apparatus, for instance, a reader, the information is read in the same manner, namely row by row. This requires reference indicia, that is, special holes which are punched at a spacing corresponding to the spacing of the rows, and which determine the sequence in which the rows are scanned and read. Such reference rows must be provided over the entire length of the data carrier, be it a tape or card and evidently results in a weakening of the carrier beyond what is inherently necessary due to the position of the rows of encoded data bits. Naturally, it is not desirable to weaken the carrier more than is absolutely necessary. Aside from this, the provision of these additional reference indicia causes extra work.
There are known so-called edge-punched cards or tapes which require that they be inserted in a proper predetermined position into the reader. In other words, such cards or tapes cannot be inserted into the reader with their underside facing upwardly, when the reader is constructed to accept them only with the underside facing downwardly, because this would result in a reversal of the locations of the left-hand and right-hand margin or edges. If, on the other hand, the reader is to be capable of accepting carriers of this type even if such reversal takes place, then the reader must be so constructed as to have two scanning devices each associated with one of the sides or margins, and with electronic means being provided to switch on that scanning device located at that side at which the punched margin or edge of the carrier is located in a given instance, while the other scanning device must remain switched off, and which electronic means must be capable of reversing the switching operation if, for instance, the next carrier is inserted in a reverse relationship from the previous one. It is hardly necessary to point out that this evidently will lead to difficulties in the first instance, in which only a single scanning device is provided and in which, if the carrier is inserted in improper relationship, the scanning device will be confronted by the margin which is not punched, and that in the second instance the construction of the reader must be rather more complicated and expensive than would otherwise be the case.
Still another disadvantage of the known data carriers of the type herein discussed is that it is difficult, if at all possible, to properly read the encoded data or information if the carrier is inserted into the reader in end-for-end reversed relationship. In other words, usually such carriers have one end which is the leading end and is intended to be inserted first into the reader; if the trailing end is instead inserted first, then the difficulties exist in reading the encoded data. Attempts have been made in the art to overcome this by providing the entire encoded data twice, with one set of such data so arranged that it can be properly read by the reader if the carrier is inserted with its leading end first, and with the other set being provided in mirror-reversed relationship to the first set and so arranged that it can be properly read if the carrier is inserted with its trailing end first. Only one of the sets is, of course, read at a time. Here it will be immediately evident that each carrier must be provided with two sets of identical information, and that this results in increased expenses for the encoding process.